Headlight knob question
 

Hello all. I'm looking for a headlight knob for a gift for my brother. He has a yellow 76 Marquis Brougham with an ugly yellow/brown interior, and the only thing missing when he got it was the headlight knob. I don't know if I need the black one or the white one. I also don't know what length of a shaft I need. If anyone could help me out it would be greatly appreciated.
Thanks!